1. Field of the Invention
The present invention relates to a packing to be suitably used as a gland packing used at an axial sealing portion of a fluid device, and also relates to a method of producing such a packing.
As a gland packing used for preventing a fluid from leaking along the outer peripheral surface of a rotary shaft in a fluid device, there is known, for example, an arrangement in which a ring-like packing is disposed at an annular space between a rotary shaft and a packing box disposed at the outer periphery thereof and in which a packing gland is used to prevent the packing from being axially moved to, thereby maintain the packing at a predetermined position.
2. Discussion of the Prior Art
The following packings are known as the packing of the above-mentioned type to seal the shaft of a fluid device. One packing is made by winding a tape-like packing material spirally or concentrically and pressing and molding, in molds, the packing material thus wound, thereby to form a ring-like packing of the die-mold type. Another packing is made by punching ring-like pieces from a sheet-like packing material, and laminating and molding a plurality of ring-like pieces thus punched, thereby to form a packing of the laminate type. A further packing is made by cutting a packing material into narrow tapes, braiding the tapes thus cut to form a braided body, and winding the braided body, as a braided packing, on the outer peripheral surface of a shaft.
In such conventional packings, the inner diameter of the packing of the die-mold type is determined at the production step. This prevents the same packing from being used for each of the shafts having different diameters. Thus, such a packing lacks versatility. It is therefore required to previously prepare a variety of packings having different diameters in order to deal with shafts having different diameters.
Further, such a packing is arranged such that layers are formed in the radial direction. This tends to produce an axial slip of the layers between adjacent layers. This causes portions of the packing to protrude into gaps, for example, between the shaft and the packing box, between the shaft and the packing gland and between the packing box and the packing gland. This reduces the volume of the packing with a consequent stress release, causing the sealing properties to be lowered. This disadvantageously increases the amount of leakage of a fluid.
It is possible to use tape-like materials having different characteristics as impregnated with, for example, a lubricant in order to enhance the lubricating properties of the packing. Even in this case, however, the tape-like materials cannot be exposed to the inner peripheral surface of the packing in order that the tape-like materials come in contact with a shaft. Thus, high lubricating properties cannot be assured.
The packing of the laminate type is arranged such that layers are formed in the axial direction. This prevents portions of the packing from protruding into the gaps mentioned above, as done in the packing of the die-mold type. This eliminates the stress release due to reduction in volume. Accordingly, the decrease in sealing properties is small. Further, the tape-like materials respectively having different characteristics, may be exposed onto the inner peripheral surface of the packing, so that the materials come in contact with the shaft, thus assuring high lubricating properties and the like, likewise the packing of the die-mold type. However, the packing of the laminate type lacks versatility since the same packing cannot be used for each of shafts having different diameters. It is therefore required to previously prepare a variety of packings to deal with shafts having different diameters. Further, when the inner peripheral surface (inner peripheral portion) of the packing which slides on and comes in contact with the shaft, is worn, the packing cannot follow the shaft satisfactorily. This disadvantageously presents the problem that the sealing properties are gradually lost with the passage of time.
As compared with these packings of the die-mold type and the laminate type, the braided packing may be cut into a predetermined length according to the diameter of the shaft and wound on the outer peripheral surface of the shaft. This improves the versatility with respect to the shaft diameter. However, braiding itself is complicated and requires a number of production steps, thus lowering the productivity. Further, it is required to use yarn that is excellent in tensile strength and toughness. This imposes great restrictions on the scope of yarn to be, used, thus increasing the cost.
These conventional packings mentioned above are not satisfactory in view of the need to dissipating heat developed at that portion of each packing which slides on the shaft. This may provoke a decrease in sealing properties due to thermal deterioration, seizure and the like.